Classifications

• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F13/00—Interconnection of, or transfer of information or other signals between, memories, input/output devices or central processing units
  • G06F13/38—Information transfer, e.g. on bus
  • G06F13/40—Bus structure
  • G06F13/4004—Coupling between buses
  • G06F13/4027—Coupling between buses using bus bridges
  • G06F13/404—Coupling between buses using bus bridges with address mapping
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F12/00—Accessing, addressing or allocating within memory systems or architectures
  • G06F12/02—Addressing or allocation; Relocation
  • G06F12/0223—User address space allocation, e.g. contiguous or non contiguous base addressing
  • G06F12/0284—Multiple user address space allocation, e.g. using different base addresses
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F13/00—Interconnection of, or transfer of information or other signals between, memories, input/output devices or central processing units
  • G06F13/14—Handling requests for interconnection or transfer
  • G06F13/16—Handling requests for interconnection or transfer for access to memory bus
  • G06F13/1668—Details of memory controller
  • G06F13/1684—Details of memory controller using multiple buses
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F13/00—Interconnection of, or transfer of information or other signals between, memories, input/output devices or central processing units
  • G06F13/14—Handling requests for interconnection or transfer
  • G06F13/36—Handling requests for interconnection or transfer for access to common bus or bus system
  • G06F13/368—Handling requests for interconnection or transfer for access to common bus or bus system with decentralised access control
  • G06F13/374—Handling requests for interconnection or transfer for access to common bus or bus system with decentralised access control using a self-select method with individual priority code comparator

Definitions

• This invention is generally related to computer systems having an input/output (I/O) subsystem in a multiple bus architecture, and more specifically to accessing an I/O messaging unit from a secondary bus.
• I/O input/output
• FIG. 1 illustrates an exemplary multiple bus computer system 100 featuring an intelligent I/O subsystem 110.
• the computer system 100 of Figure 1 is based on the industry-standard Peripheral Components Interconnect (PCI) specification generally defined by the PCI Special Interest Group in PCI Local Bus Specification, Revision 2.1, October 21, 1994.
• PCI Peripheral Components Interconnect
• the system features two physically separate PCI system busses, primary PCI bus 114 and secondary PCI bus 118.
• a bridge unit 126 combines the two system busses into one logical bus having a single PCI address space that is compliant with the PCI-to-PCI Bridge Architecture Specification, Revision 1.0, also published by the PCI Special Interest Group, April 5, 1994.
• Agents such as host processor 164 and peripheral devices such as first PCI agent 172 and second PCI agent 176 reside on the system busses and communicate transparently with each other through the bridge.
• a local bus 122 is coupled to the system busses via the primary and secondary address translation units (P_ATU 134, S_ATU 146).
• the ATUs support transactions between the PCI address space and the I/O subsystem local address space.
• a subsystem processor 152 and memory controller unit (MCU) 156 coupled to a local memory communicate with each other using the local bus 122.
• the subsystem processor 152 and local memory bring intelligence to the I/O subsystem by processing the I/O message tasks at the I/O subsystem level versus the host processor 164 level.
• the I/O subsystem also includes an I/O messaging unit (MU) 130 which is closely coupled to or, alternatively, a part of the P_ATU 134.
• the MU facilitates I/O transactions, i.e. the transfer of data between the PCI agents on the primary bus and the subsystem processor and local memory.
• the MU provides for data transfer between the host operating system and the I/O subsystem through the posting of requests and completions of I/O transactions.
• I/O transactions involve the transfer and performing of I/O messages that comply with the Intelligent I/O (I 2 O®) Architecture Specification, Version 1.5, March 1997.
• the specification is designed to simplify the task of building and maintaining high performance I/O systems.
• the I 2 O specification provides a common I/O device driver and I/O (or I 2 O) protocol that is independent to both the specific control device and the host operating system.
• the I 2 O specification supports message passing between agents and the I/O subsystem. These I/O messages typically specify operations to be performed by the subsystem processor 152 and MCU 156. Such messages are described in the I 2 O specification and are of a higher level format than conventional read and write transactions, and may include multiple PCI and/or local bus read and write transactions. For example, an I/O message may contain a sequence of transactions that request the I/O subsystem to read data
• I/O message that provides an agent with the address information required for performing a transaction with another agent on the primary PCI bus 114.
• Such a message is typically used by a peripheral device to communicate with another device while bypassing the host processor 164.
• the host processor 164 is configured (through the host operating system and other software) to place the I/O messages in host memory 168, and initialize the MU 130 by providing pointers to the I/O messages. These pointers are stored in message queues and are accessed through the MU 130.
• the MU guarantees a fixed address range on the primary bus which may be used by the PCI system and the I/O subsystem to access the pointers and the I/O messages.
• the message queues may be stored in host memory 168, or in I/O memory 160 and may be accessed via the MU 130 in response to I/O requests received from agents on the primary bus 114 and from the subsystem processor 152.
• the conventional mechanism for processing I/O requests by the MU involves only the P_ATU 134 and the primary PCI bus 114.
• Each ATU normally provides a two-way communication and data flow path between the local bus 122 and the corresponding PCI system bus.
• the ATU implements an address windowing scheme to determine which requests are to be claimed and translated to the appropriate bus.
• Transactions where a PCI bus master, such as PCI agent 164, is accessing the local bus 122 through the ATU are called inbound transactions.
• Each ATU may be programmed to define an inbound address translation window, where requests having PCI addresses within the window are claimed by the ATU and translated into a local bus address.
• the MU 130 uses a portion of the primary inbound translation window of the P_ATU 134 to respond to I/O requests, as distinguished from other requests that seek transactions involving the local bus 122, from agents on the primary bus 114.
• the MU also uses the PCI configuration registers of the P_ATU for control and status information.
• the I/O requests are typically initiated by the host processor 164 or other agent 172 on the primary PCI bus 114, and directed to the MU portion of the primary inbound translation window.
• an intelligent agent on the secondary PCI bus 118 does not have direct access to the MU 130 or the I 2 O protocol. Rather, the agent on the secondary bus requests the host processor (through the bridge 126) to perform the I 2 O protocol on its behalf. This increases the burden on the host processor, especially as the number of intelligent agents on the secondary bus 118 increase.
• a mechanism is desirable which allows the intelligent agent on the secondary bus to directly access the MU 130 in order to perform the I 2 O protocol while minimizing interaction with the host processor 164.
• such a mechanism should allow agent software that employs the I 2 O protocol to be portable, i.e., applicable without significant modifications, as to requests originating from both the primary and secondary busses.
• agents on both busses should be able to access the same amount of local memory in preferably the same address space when interfacing through the ATUs, so that the agents may be moved from one bus to another without the need for reconfiguring the software in each agent.
• the mechanism should not require knowledge by the agents of which bus they are located on before they are able to properly implement the I 2 O protocol.
• the mechanism for accessing the messaging unit should sacrifice the least amount of PCI addresses given the constraint of fixed address space boundaries in the PCI bus specification.
• One possible technique that may facilitate I 2 O transactions from the secondary bus would be to add a second MU closely coupled to the S_ATU 146.
• the second MU would perform substantially the same as the messaging unit 130 in Figure 1, except that the second MU would be configured to claim a portion of the S_ATU address space.
• This dual MU architecture may present an additional problem when combined with the need for maintaining portability in agent software by requiring that the P_ATU and S_ATU address translation window (including the address range for the first and second MUs) to be the same.
• Having identical address translation windows for the P_ATU 134 and S_ATU 146 may require a scheme to manage several pairs of message queues in the MUs simultaneously, because there would exist a pair of pointers to the same I/O message, i.e., two pointers to the same location in host memory.
• This mechanism would require an additional data coherency protocol to support the dual MU mechanism.
• Such a coherency mechanism would require one MU to "snoop" or be aware and observe the actions of the other MU.
• the silent MU would be required to invalidate some of its available message pointers to data, due to the activity of the other MU performing a valid transaction with the same data.
• a potentially complex data coherency issue arises when using such a dual MU design to achieve portability in PCI agent software.
• This invention in one embodiment is directed at a data processing device having a processor, a bridge unit, and a messaging unit (MU).
• the bridge unit is for coupling a primary bus to a secondary bus and, in particular,
• the bridge is configurable to claim requests that access an MU address range from the secondary bus.
• the MU is configured to interrupt the processor in response to receiving a request to invoke a message, where the request accesses the MU address range and is initiated on the secondary bus.
• the processor is configured to access the message and then execute a number of instructions related to the message.
• Figure 1 illustrates a computer system suitable for implementing an embodiment of the invention.
• Figure 2 illustrates the address spaces used for defining an embodiment of the invention.
• Figure 3 is a flow diagram of the steps to be performed in a computer system according to another embodiment of the invention.
• the invention is directed to a data processing device which allows agents on a secondary bus of a multiple bus computer system to access a messaging unit (MU) which resides on the primary bus of the computer system.
• MU messaging unit
• a particular embodiment of the invention may be implemented using the PCI architecture and the I 2 O specification. That particular embodiment allows the I 2 O protocol to be performed between agents or devices on either the primary or secondary PCI bus and the I/O subsystem.
• access to the MU from either the primary or secondary bus is virtually identical in the sense that the same address range is used from either primary or secondary bus to access the MU .
• a data processing device includes some of the functional blocks of the I/O subsystem 110 shown in Figure 1.
• the data processing device may be a so-called I/O processor single integrated circuit having interfaces to a primary PCI bus 114 and secondary PCI bus 118, local bus 122, and local memory.
• a subsystem processor 152 is featured within the I/O subsystem 110 which couples to the local bus 122.
• the I/O subsystem 110 may also include a memory controller unit (MCU) 156 on the local bus 122.
• the MCU 156 handles all transactions on the local bus 122 that seek access to the I/O memory 160.
• the local bus 122 is shown to extend beyond the I/O subsystem 110 boundary in Figure 1, the bus may alternatively lie entirely within the I/O subsystem 110 boundary, confined to the single IC as an internal bus of the I/O processor embodiment.
• a bridge unit 126 is also included in the I/O subsystem 110 for coupling the primary to the secondary busses.
• the bridge unit 126 may be enabled to claim requests on the secondary bus for accessing the MU 130 address range, for example, in response to at least one enable bit in a register of the I/O subsystem 110 being toggled. Such an enable bit may be part of the configuration registers of the bridge unit 126 or the I/O subsystem 110.
• Communication between the PCI system busses and the local bus 122 is accomplished through the primary and secondary address translation units (ATUs).
• Each ATU is configured to convert addresses of requests from the PCI system bus to the local bus 122, and vice versa.
• Each ATU has an address translation window which defines the range of requests that are claimed by the ATU.
• the PCI address space of the computer system 100 in Figure 1 includes a common ATU translation window that is used by the agents on the primary and secondary busses to initiate transactions with the I/O subsystem and the local bus.
• Figure 2 illustrates the translation between the local and PCI address spaces performed by the P_ATU 134 and S_ATU 146, as well as the preferred range of the address translation windows and the location of the MU address range. Having the P_ATU 134 and S_ATU 146 share a common translation window, except for the MU range, will allow device driver software used for accessing the I/O subsystem to be portable between devices on either the primary or the secondary busses.
• Figure 2 also shows the preferred MU range as being a part of the P_ATU translation window. The portion of the inbound translation window of the P_ATU 134 and S_ATU 146 that is not the MU range may be used for PCI transactions that access the I/O memory.
• the I/O subsystem is configured such that whenever the bridge is enabled to claim the MU range on the secondary bus, the MU range ceases to be part of the S_ATU translation window. This may be controlled by an enable bit of the I/O subsystem 110. The bit may be part of the configuration registers of the bridge 126. When so enabled, transactions initiated on the secondary bus accessing the S_ATU translation window will still be forwarded to the local bus through the S_ATU 146, but I/O requests within the MU address range are not claimed by the S_ATU 146. Instead, the bridge unit claims those I/O requests on the secondary bus, and forwards them to the primary bus where
• the MU 130 will also respond to requests that are generated on the primary bus, for example by the host processor 164, provided the requests also access the MU address range.
• Some of the mechanisms in the MU for message processing include message registers and circular queues.
• the message registers are used by the I/O subsystem to send and receive messages. When written, these registers may cause an interrupt to be generated to either the subsystem processor or the primary or secondary PCI busses.
• the MU also has a number of circular queues, at least one for inbound messages and at least one for outbound messages.
• Inbound messages are those that are "posted" by an agent from either the primary or secondary bus, whereas outbound messages are those posted by the subsystem processor, to be processed by other processors or agents on the PCI busses.
• the circular queues contain pointers to locations in I/O memory which in turn contain pointers to where the actual I/O message may be found. An exemplary relationship between the pointers may be seen in Figure 1.
• the I/O subsystem includes logic circuitry that allows a primary interface of the I/O subsystem that is logically distributed as shown in Figure 1 to act as a master and a slave during the same transaction.
• the primary interface is shown as dotted circles coupled to the primary bus and in this embodiment serves the I/O subsystem as a whole, including the individual MU, P_ATU, and bridge units.
• bridge-like functions such as forwarding a request from the secondary bus to the primary bus
• the primary interface is configured to be a master on the primary bus when performing a request on behalf of an initiator. If the request contains an I/O message destined to the MU, then the primary interface will then be configured as a slave to receive the request.
• the primary interface behaves as both a master and a slave in the same transaction, where the transaction includes a request to perform an I/O message.
• I/O subsystems Some system applications of the I/O subsystem embodiment described above include peer-to-peer technology (allowing peripheral devices or "cards" on a PCI bus to communicate with each other), on-line storage backup and remote storage backup systems, file servers, database servers, World Wide Web (Web) servers, intranet servers, and on-line transaction processing systems.
• Figure 1 may be used to illustrate an embodiment of the invention as a network server motherboard.
• the I/O subsystem operates the same as described earlier, where in particular the I/O subsystem contains special decode circuitry that allows the S_ATU 146 to not claim the MU address range, and instead allowing the bridge unit 126 to claim requests on the secondary bus that access the MU address range.
• the requests on the secondary PCI bus 118 will in this case be generated by a network interface controller depicted as the second PCI agent 176 and may invoke an I/O message that attempts to transfer a block of received data to the host memory.
• the I/O message would be stored, for example, in the agent memory 170.
• the second PCI agent 176 on the secondary bus may be a mass storage controller such as a disk controller.
• the disk controller has access to the I 2 O protocol and can cause data to be transferred between the host memory and itself, without the need for intervention by the host processor, using the MU address range claimed by the bridge.
• the agent After making such a determination, the agent initiates a request according to the I2O protocol on the secondary bus to access the MU address range and post a first I/O message in the MU. As indicated earlier, the agent has the intelligence to select an I/O message from a number of messages that exist in the I2O protocol. These messages have been configured into the computer system, either in host memory or agent memory, during a prior initialization scheme.
• the bridge After the bridge receives notification of the request on the secondary bus, the bridge determines if the request falls within the MU address window. This window may also be preconfigured by the host processor during the initialization scheme. After claiming the request, the bridge may forward the request to the secondary bus.
• the request includes the information needed to identify the address of the I/O message, in either host memory 168, or agent memory 170.
• the S_ATU 146 which normally translates all PCI requests within its translation window on the secondary bus into requests on the local bus 122, is configured not to claim requests that are within the MU address range. Thus, the request is not forwarded from the secondary bus directly to the local bus 122.
• the MU may claim the request and the I/O message is posted in the MU.
• the I/O message is posted by writing the address of the I/O message (pointer to the I/O message) to a circular queue having an address in the MU range.
• the request may initially be claimed by the P_ATU and then handed off to the MU.
• the MU notifies the subsystem processor of *he posting.
• the subsystem processor may then read the pointer from the MU, and then accesses the I/O message, which at the time may be stored in the agent memory.
• the I/O subsystem (through the MU) may transfer the I/O message from agent memory 170 to I/O memory 160, via the direct memory access (DMA) units 138 or 142.
• DMA direct memory access
• the subsystem processor ultimately performs the I/O message by accessing instructions and data that are part of the I/O message.
• the memory controller may also be called upon by the subsystem processor to help perform some of the instructions in the message, such as transfer data to and from the I/O memory.
• the embodiments of the invention described above allow agents such as intelligent PCI agents on a secondary PCI bus 114 to access an MU 130 which resides on the primary bus of a multiple bus computer system having an I/O subsystem.
• This mechanism allows the industry standard I2O® protocol to be performed between devices on either the primary or secondary bus and the I/O subsystem. Access to the MU from either primary or secondary bus becomes similar as far as the initial I/O request is concerned, permitting portable MU accessing software to be written.
• the I/O subsystem is configured with special decode circuitry that allows the S_ATU to not claim an
• the bridge thus forwards all such requests to the primary bus, where the MU may claim the request, and notify the subsystem processor that an I/O message has been posted.
• the P_ATU 134 and S_ATU 146 are programmed to cover the same address translation window. In this way, agents on either the primary or secondary busses may access the MU 130 and the I/O memory 160 using the same initial request, thereby allowing agents to be moved from one bus to the other without having to reconfigure the MU accessing software in each one.
• the I/O messages may be stored in either the host memory 168 or the agent memory 170, and then be transferred to I/O memory 160 before being performed by the subsystem processor.
• the actual MU address range may be selected and programmed according to system application requirements.
• a network server implementation of the invention may employ a large number of I/O messages and a large part of the I 2 O protocol, and therefore require a greater number of addresses in the MU address range than would a workstation. Therefore, the scope of the invention should be determined not by the embodiments illustrated but by the appended claims and their legal equivalents.

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• 1998
  • 1998-02-13 US US09/023,494 patent/US7007126B2/en not_active Expired - Fee Related
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